The present invention relates to an enlarging/smoothing processor for enlarging and smoothing image data, and more particularly to an enlarging/smoothing processor capable of shaping reproduced characters and figures so as to take natural forms.
In the field of the image processing technology, the technique to enlarge original image data and to print out the enlarged image data by a printer has been put into practical use. When the image data is simply enlarged, notches appear on oblique portions of characters and figures. The notches impair the print picture quality. To avoid this picture quality deterioration, the process for removing the notches, viz., smoothing process, is indispensable.
There are proposed some smoothing techniques as disclosed in Japanese Patent Unexamined Publication Nos. Sho. 60-11885 and Hei. 1-208154.
In the most popular facsimile machine of G3 mode, two resolutions are applied for the received image data under the recommendation of CCITT (International Telegraph and Telephone Consultative Committee); one is a standard resolution of 8 pixels/mm.times.3.85 lines/mm and the other, a high resolution of 8 pixels/mm.times.7.7 lines/mm.
Further, the facsimile machines of high resolution and high line densities are recently marketed. In some facsimile machines of G3 mode, 16 pixels/mm.times.15.4 lines/mm, and in some facsimile machines of G4 mode, a plurality of resolutions are used, which are selected from among 200 dpi, 240 dpi, 300 dpi and 400 dpi.
The facsimile machine with a plurality of resolutions contains a recording device of a higher resolution. To record such image data as to have a resolution lower than that of the recording device, the image data is enlarged before recorded. The reason for this is that if the image data of low resolution is recorded as it is by the high resolution recording device, the image is recorded in the reduced form.
For example, when the received image data of the standard resolution, 8 pixels/mm.times.3.85 lines/mm, is recorded by a recording device of 400 dpi, the image is halved in the fast scan direction and is quartered in the slow scan direction. Accordingly, to record the received image data of the resolution, 8 pixels/mm.times.3.85 lines/mm, by a recording device of 400 dpi, the received image data must be enlarged to be approximately two times as large as the original one in the fast scan direction, and to be approximately four times in the slow scan direction.
The technique to record the image data of low resolution by the recording device of high resolution after the image data is enlarged is disclosed in Japanese Patent Unexamined Publication Nos. Sho. 62-25565 and 62-60358, for example.
To execute the smoothing technique, a high level interpolation process using an increased number of reference pixels adjoining to a marked pixel must be carried out at a high speed and at an optional enlargement ratio is required for the smoothing process. However, the conventional smoothing processor cannot carry out such a high level interpolation process.
Additionally, the conventional image processor further suffers from the following problems. It is difficult to smooth steeply oblique lines. The smoothing process makes lines fat, deteriorates the picture quality, and deforms the right-angled corner.